Evolution and Ecology: The Pace of Life
K.D. Bennett 1997 Cambridge University Press

This book deals with punctuated-equilibrium evolutionary mechanisms during the Quaternary. The author argues that frequent (on a scale of tens of thousands of years) ice ages and related climate shifts would have made gradual speciation difficult or impossible. Changing conditions (even if populations migrated to deal with climate changes) disrupted gradually-accumulating genetic differences between populations that could have led to speciation. So, many species remained unchanged and new ones necessarily originated rapidly.